1. Mechanical Advantage and Efficiency

2. Mechanical Advantage
A machine’s MA is the number of times a force exerted on a machine is multiplied by the machine.
The MA is a ratio between the output and input force
MA = Output Force / Input Force

3. Question
If you exert a force of 20 N on a can opener, and the opener exerts a force of 60 N on the can, the ideal mechanical advantage of the can opener is 6 2
1200 3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

4. Mechanical Advantage > 1
A machine with a mechanical advantage of greater than 1 multiplies the input force.
Examples: can opener
a ramp

5. Mechanical Advantage < 1
A machine with a mechanical advantage of less than 1 does not multiply the force but increases the distance and speed.
Example: Hockey Stick
Paper Fan

6. Mechanical Advantage = 1
A machine with a mechanical advantage of 1 means that a machine changes the direction of the force.
Example: Rope

7. Question
The mechanical advantage of a machine that changes only the direction of force is 1
Less than 1
Greater than 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

8. Principle of Conservation of Energy
No machine can increase both the magnitude and the distance of a force at the same time.

9. Efficiency of Machines
To calculate the efficiency of a machine, divide the output work by the input work and multiply the result by 100 percent.
Efficiency = Output work * 100%
Input work

10. The efficiency of a machine compares
Question
The efficiency of a machine compares
Force to mass
Output work to input work.
Force to friction
Friction to mass 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

11. Actual Mechanical Advantage
The actual mechanical advantage is the mechanical advantage that a machine provides in a real situation.

12. Ideal Mechanical Advantage
The ideal mechanical advantage is the mechanical advantage of a machine without friction.
The more efficient a machine is, the closer the actual mechanical advantage is to the ideal mechanical advantage.

13. An ideal machine would have an efficiency of
Question
An ideal machine would have an efficiency of
1 percent
10 percent
50 percent
100 percent 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

14. Question
If tight scissors have an efficiency of 50 percent, how much of your work is wasted overcoming friction?
All of it
None of it
One half of it
10 percent of it 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

15. Without friction there would be
Question
Without friction there would be
Less machine efficiency.
Greater output work than input work.
Greater input work than output work.
Equal input and output work. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

16. Simple Machines
Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work against those forces.

17. Simple Machines The six simple machines are: Lever Wheel and Axle
Pulley
Inclined Plane
Wedge
Screw

18. Simple Machines
A machine is a device that helps make work easier to perform by accomplishing one or more of the following functions:
transferring a force from one place to another,
changing the direction of a force,
increasing the magnitude of a force, or
increasing the distance or speed of a force.

19. The 6 Simple Machines Screw Wedge Inclined Plane Pulley Wheel and Axle
Lever

20. Inclined Plane

21. Inclined Plane
The Egyptians used simple machines to build the pyramids. One method was to build a very long incline out of dirt that rose upward to the top of the pyramid very gently. The blocks of stone were placed on large logs (another type of simple machine - the wheel and axle) and pushed slowly up the long, gentle inclined plane to the top of the pyramid.

22. Inclined Planes
An inclined plane is a flat surface that is higher on one end
Inclined planes make the work of moving things easier
A sloping surface, such as a ramp. An inclined plane can be used to alter the effort and distance involved in doing work, such as lifting loads. The trade-off is that an object must be moved a longer distance than if it was lifted straight up, but less force is needed. You can use this machine to move an object to a lower or higher place.  Inclined planes make the work of moving things easier.  You would need less energy and force to move objects with an inclined plane.  22

23. The Lever
A lever is a rigid bar that rotates around a fixed point called the fulcrum.
The bar may be either straight or curved.
In use, a lever has both an effort (or applied) force and a load (resistant force).

24. There are 3 Classes of Levers
Depends on the location of 3 items:
1. Fulcrum – fixed point on a lever
2. Effort Arm – the part of the lever that exerts the effort force.
3. Resistance Arm – the part of the lever that exerts the resistance force (where the load is).
 EA 
RA

25. 1st Class Lever Changes the direction of the force
Multiplies effort force
Magnifies speed and distance
Ex: seesaw, crowbar, scissors

26. 2nd Class Lever Multiply effort force
Mechanical advantage is always greater than 1.
Ex: bottle opener, boat oars, wheel barrow

27. 3rd Class Lever Magnifies speed and distance
Mechanical Advantage always less than 1
Ex: baseball bat, golf club, broom, shovel

28. WHEEL AND AXEL
The axle is stuck rigidly to a large wheel. Fan blades are attached to the wheel. When the axel turns, the fan blades spin.

29. Pulleys Pulley are wheels and axles with a groove around the outside
A pulley needs a rope, chain or belt around the groove to make it do work

30. Diagrams of Pulleys Movable Pulley: Fixed pulley:
A fixed pulley changes the direction of a force; however, it does not create a mechanical advantage.
Movable Pulley:
The mechanical advantage of a moveable pulley is equal to the number of ropes that support the moveable pulley.

31. COMBINED PULLEY
The effort needed to lift the load is less than half the weight of the load.
The main disadvantage is it travels a very long distance. 

32. Pulleys

33. Mechanical Advantage Ratio of Output Force to Input Force
The Mechanical Advantage is calculated by dividing the Output Force by the Input Force. This is used for ANY simple machine. After the trials for 1-6 strings have been completed it is time to look at the results obtained. It becomes clear that the more strings used to support the load, the force needed to lift the load decreases. We call this an Inverse Relationship. The relationship between the mechanical advantage and the # of strings supporting the load may become much clearer at this point.
Ratio of Output Force to Input Force
Follows simple pattern with Ropes and Pulley system

34. Rube Goldberg Machines
Rube Goldberg machines are examples of complex machines.
All complex machines are made up of combinations of simple machines.
Rube Goldberg machines are usually a complicated combination of simple machines.
By studying the components of Rube Goldberg machines, we learn more about simple machines

35. More about the Pulley What is a pulley? A pulley is a wheel
A pulley uses rope that goes around the pulley in its groove
The rope attaches to objects
Force is applied to the other end of the rope

36. Why use a pulley wheel and not just rope looped around the beam?
Imagine this scene without a pulley.
Can the hay be lifted in some way with just rope?
Why use a pulley wheel?
The pulley reduces the amount of friction, making the job easier!

37. 1. Fixed Pulley Object moves Pulley stays in the same spot
Force
Rope
Fixed Pulley
Object moves
Pulley stays in the same spot
Force applied only on one end of the rope
Weight

38. Single Fixed Pulley
Is mechanical advantage provided with this system? No
The effort needed to lift this load is equal to the weight of the load.
This is because the load is supported by only 1 rope arm.
You must also pull an amount of rope equal to the height you wish to lift the load.
This pulley provides the user with Directional Advantage (allows you to pull down), allowing someone to pull down to lift the load up.

39. How much effort then would it take to lift this load?
The farmer must use an effort equal to the weight of the load.
Remember, there is no mechanical advantage here…

40. 2. Movable Pulley Movable Pulley Pulley and object move together
Reaction
Force
Movable Pulley
Pulley moves along the rope
Pulley and object move together
Wheel supports the load
Rope is attached to something that does not move
Reduces the force needed to move the object
Rope
Force
Pulley
Weight

41. Single Moveable Pulley
It requires only ½ the effort to lift the load because there is more than 1 rope arm.
If the load here ways 20 lbs., only 10 lbs. are needed to lift it.
You must pull twice as much rope to lift the load to a certain height.
Example: Pull 2 ft. of rope for each 1 foot of height you want to lift the load.
This pulley system provides mechanical advantage!

42. More ropes – More advantage
In the second picture, the weight is held by two ropes instead of one. That means the weight is split equally between the two ropes, so each one holds only half the weight.

43. We know the facts…but do we know why?
Why is the force needed to lift the load less when you have more pulleys?

44. How did you do? Analogy: Think of it this way…
If you pick up a load, like a bag of books, that weighs 100 N with one hand, all of the force is directed down one arm. The force acting on the arm is 100 N, counteracting the pull of the books.
If you reach down with the other hand and hold the bag of books with two hands, the books still pull with 100 N of force, but the lifting force is distributed between 2 arms. Each arm is pulling with a force of 50 N.

45. 3. System of Pulleys System of Pulleys Has at least two wheels
The more complex the pulley, the more the effort needed to move the object decreases
The force needed to raise this weight is ¼ the weight of the object.
Weight

46. 3. Combined (double) Pulley:
This pulley system combines the single fixed & single moveable and their properties giving you both
Directional & Mechanical Advantage
This pulley provides directional advantage (allows you to pull down to lift the load)
It also provides mechanical advantage by using 2 rope arms (which reduces effort needed to lift the load)
In this system, you would pull 2 times as much rope for every unit of height you that you want to lift the load.

47. Pulley Systems

48. Pulleys are used to gain mechanical advantage, trading the amount of rope you have to pull to lift an object for how heavy the object can be.

49. The more lines of support (ropes) a pulley has, the more mechanical advantage it has!

50. Who has seen pulleys? …Pulleys are all around us…  Elevator
Flagpole 
 Window shades and blinds

51. More examples  Cranes   Sails and fishing nets + clothes lines
+ gym training equipment
+ rock climbing gear

52. Why use pulleys? Makes lifting things easier Pulleys
Enables us to use gravity to help us (it is usually easier to pull down to lift something up – directional advantage)
Using several pulleys reduces the force required to lift an object
We have to use more rope and make the rope go further
Mechanical Advantage: More distance traveled, but less force required

53. Using Gravity Easier to pull down than up Elevators use gravity
Elevator Pulleys
Easier to pull down than up
Elevators use gravity
Counterweight on the other side of the cable
Gravity already applying force on counterweight
Less powerful motor required
Counterweight

54. Vocabulary & Definitions
Force: A push or pull on an object
Fixed pulley: A pulley attached to a fixed point with the rope attached to the object
Movable pulley: A pulley attached to the object itself, with one end of the rope attached to a fixed point
Mechanical advantage: The advantage gained by using simple machines; reduced effort
Directional advantage: Pulleys can change the direction that the effort is applied

55. Pulley Power!
Single fixed pulleys – provide directional advantage you can use counter-weights to reduce your effort but…
effort + counter weight must be = or more than the weight of the object being lifted
Single movable pulleys – provide mechanical advantage you must pull 2 times the distance of rope because the load is supported by 2 rope arms
Compound pulley systems - – provides directional & mechanical advantage the more rope arms supporting the load the greater the mechanical advantage

56. Homework
Mechanical Advantage Worksheet:
Questions 2,6,7,10,12